This invention relates generally to golf balls, and more particularly to wound golf balls, having an improved center covered with elastomeric thread wound using a novel winding tension.
Golf balls can be divided into several general categories, such as solid golf balls having one or more layers and wound golf balls. Solid golf balls include both one-piece and two-piece balls. One-piece golf balls are easy to construct and relatively inexpensive, but are considered by most to have poor playing characteristics. These golf balls are generally limited for use as range balls. Two-piece balls are typically constructed with a solid polymeric core encased with a cover and are generally the most popular with recreational golfers because they are very durable and provide maximum distance. Typically, the core is formed from polybutadiene that is chemically crosslinked with zinc diacrylate and/or other similar crosslinking agents. Two-piece balls are generally easy to manufacture, but are regarded as having limited playing characteristics. Solid golf balls also include multi-layer golf balls that are comprised of a solid core of one or more layers and/or a cover of one or more layers. These balls are regarded as having an extended range of playing characteristics.
Wound golf balls are the preferred ball of more advanced players due to their high spin and soft xe2x80x9cfeelxe2x80x9d characteristics. Wound golf balls typically include a solid, hollow, or fluid-filled center surrounded by a tensioned elastomeric material and a cover, the combination of which results in a wound core. The wound core is then covered with a durable cover material, such as a Surlyn(copyright), or a softer xe2x80x9cperformancexe2x80x9d cover, such as balata or polyurethane.
Wound golf balls are generally softer in xe2x80x9cfeelxe2x80x9d and provide more spin than solid golf balls, which enables a skilled golfer to have more control over ball flight. This control is especially important for approach shots into the green, where the high spin rate of soft-covered, wound golf balls enables the golfer to stop the ball very near its landing position. The higher spin rate that aids in ball control on approach shots and around the green also causes wound golf balls to sacrifice some distance compared to hard-covered, solid golf balls. However, the advantages of wound constructions over solid ones are more related to targeting and accuracy than they are to distance.
To meet the needs of golfers having various levels of skill, golf ball manufacturers are also concerned with adjusting the compression of the ball. Compression is a measurement of the deformation or deflection of a golf ball under a fixed load. A golf ball with a higher compression feels harder than a golf ball having a lower compression. Wound golf balls generally have a lower compression that is preferred by better players, to whom xe2x80x9cfeelxe2x80x9d and control are more important than distance. Whether wound or solid, all golf balls become more resilient (i.e., have higher initial velocities) as compression increases. Manufacturers of both wound- and solid-construction golf balls must, therefore, balance the requirement of higher initial velocity afforded from higher compression with the desire for a softer xe2x80x9cfeelxe2x80x9d gained by lower compression.
It is well-known in the art that to make wound golf balls, manufacturers typically use automated winding machines to stretch the threads to various degrees of elongation during the winding process, with every effort made to avoid subjecting the threads to unnecessary incidents of breakage. As the elongation and the winding tension increase, the compression and initial velocity of the ball will increase accordingly. This increase in compression and velocity result in increased distance when the wound ball is hit with a club.
There are some drawbacks to the conventional threads used in golf balls. The thread occasionally contains weak points that can break during winding or during play. When a thread breaks during manufacturing, the winding machine either needs to be restarted or, in many cases, an operator must manually re-thread the machine prior to restarting. Both of these situations decrease productivity and are obviously undesirable. The thread can also break during play due to impact of a club with the ball resulting in, for example, a loss of compression and/or initial velocity. Additionally, for a fluid-filled wound ball, a broken thread can cut through the envelope containing the fluid, destroying the structural integrity of the ball, making it virtually unplayable.
To date, golf ball manufacturers have typically combined high-tension windings with very soft centers, the theory being that the tensioned windings provide the xe2x80x9cenginexe2x80x9d for the golf ball and the soft center provides the desired xe2x80x9cfeelxe2x80x9d characteristics. As one of ordinary skill in the art knows, winding tensions are typically greater than 700 g and can be as high as 1000 g or more. Manufacturers are generally careful to limit solid center diameter to allow a sufficient amount of wound material to provide the desired resilience in the golf ball.
It would be advantageous to manufacture a wound golf ball in which the tensioned thread was wound at a lower tension to decrease thread breakage, while still retaining desirable compression, velocity, distance, and spin characteristics afforded by a harder center. A combination previously thought to be unacceptable. The present invention discloses such an advantageous golf ball.
The present invention is directed towards a wound golf ball comprising a center, a cover, and at least one wound layer disposed between the center and the cover; wherein the at least one wound layer is formed of a tensioned elastomeric thread having at least one ply, wound about the center with a tension of less than about 700 g; and wherein the center has a first deformation value, formed by applying a load to the center within the range from an initial load of 10 kg to a final load of 130 kg, and the golf ball has a second deformation value, formed by applying a load to the golf ball within the range from an initial load of 10 kg to a final load of 130 kg, such that a difference between the second deformation and the first deformation is less than 0.4 mm.
In one embodiment, the deformation difference is no greater than about 0.3 mm. In another embodiment, the tension is less than about 500 g and is preferably between about 400 g and 500 g. In still another embodiment, the first deformation value, formed by applying a load to the center within the range from an initial load of 10 kg to a final load of 130 kg, is less than 3.5 mm. Preferably, the first deformation value, formed by applying a load to the center within the range from an initial load of 10 kg to a final load of 130 kg, is no greater than about 3.1 mm.
In a preferred embodiment, the cover is a single layer. In another embodiment the cover is formed of two or more layers.
In another embodiment, the tensioned elastomeric thread comprises two or more plies. Preferably, the tensioned elastomeric thread comprises cis-polyisoprene and more preferably, a blend of cis-polyisoprene and natural rubber. In one embodiment, the tensioned elastomeric thread has a thickness of between about 0.01 and 0.06 in. In a preferred embodiment, the thickness is between about 0.018 and 0.03 in. The tensioned elastomeric thread preferably has a width of between about 0.04 and 0.08 in, and more preferably, between about 0.06 and 0.07 in.
Preferably, the center comprises polybutadiene. In one embodiment, the center further comprises a metal salt diacrylate, a free radical initiator, and a filler. In another embodiment, the center has a center diameter of greater than about 1.3 in, and more preferably between about 1.3 and 1.4 in. In a preferred embodiment, the center diameter is between about 1.35 and 1.4 in. In one embodiment, the center has a hardness of between about 60 and 90 Shore D. In another embodiment, the center has a hardness of between about 70 and 80 Shore D.
In another embodiment, the cover has a thickness from about 0.03 in to about 0.12 in and preferably about 0.04 to 0.09 in. In a preferred embodiment, the cover has a thickness of about 0.05 to 0.085 in. In still another embodiment, the cover has a Shore D hardness of greater than about 60. Preferably, the cover has a Shore D hardness of between about 63 and 73 Shore D. In one embodiment, the cover comprises a blend of about 40 to 60 weight percent of a sodium ionomer and about 60 to 40 weight percent of a zinc ionomer.
In yet another embodiment, the golf ball has an outer diameter of greater than about 1.68 in. Preferably, the center and the at least one wound layer form a core having an outer diameter of between about 1.51 and 1.62 in. In a further embodiment, the outer diameter is between about 1.55 and 1.58 in.
The present invention is also directed to a wound golf ball comprising a center, a cover, and at least one wound layer disposed between the center and the cover; and wherein the at least one wound layer is formed of a tensioned elastomeric thread of at least one ply having an elongation of less than about 800 percent.
In one embodiment, the center has a first deformation value, formed by applying a load to the center within the range from an initial load of 10 kg to a final load of 130 kg, and the golf ball has a second deformation value, formed by applying a load to the golf ball within the range from an initial load of 10 kg to a final load of 130 kg, such that a difference between the second deformation and the first deformation is less than 0.4 mm. Preferably, the deformation difference is no greater than about 0.3 mm. In a preferred embodiment, the elongation is between about 500 and 800 percent.
In another embodiment, the first deformation value, formed by applying a load to the center within the range from an initial load of 10 kg to a final load of 130 kg, is less than 3.5 mm. Preferably, the first deformation value, formed by applying a load to the center within the range from an initial load of 10 kg to a final load of 130 kg, is no greater than about 3.1 mm.
In another embodiment, the tensioned elastomeric thread has a thickness of between about 0.01 and 0.06 in. Preferably, the thickness is between about 0.018 and 0.03 in. In still another embodiment, the tensioned elastomeric thread has a width of between about 0.04 and 0.08 in. Preferably, the width is between about 0.06 and 0.07 in.
In yet another embodiment, the center has a center diameter of greater than about 1.3 in. More preferably, the center diameter is between about 1.3 and 1.4 in. Most preferably, the center diameter is between about 1.35 and 1.4 in. In a further embodiment, the center has a hardness of between about 60 and 90 Shore D. Preferably, the center has a hardness of between about 70 and 80 Shore D.
In one embodiment, the cover has a Shore D hardness of greater than about 60. Preferably, the cover has a Shore D hardness of between about 63 and 73 Shore D. In another embodiment, the center and the at least one wound layer form a core having an outer diameter of between about 1.51 and 1.62 in. In sill another embodiment, the outer diameter is between about 1.55 and 1.58 in.
As used herein, the term xe2x80x9cAtti compressionxe2x80x9d is defined as the deflection of an object or material relative to the deflection of a calibrated spring, as measured with an Atti Compression Gauge, that is commercially available from Atti Engineering Corp. of Union City, N.J. Atti compression is typically used to measure the compression of a golf ball or its components. When the Atti Gauge is used to measure cores having a diameter of less than 1.680 inches, it should be understood that a metallic or other suitable shim is used to make the measured object 1.680 inches in diameter. However, when referring to the compression of a core, it is preferred to use a compressive load measurement. The term xe2x80x9ccompressive loadxe2x80x9d is defined as the normalized load in pounds for a 10.8-percent diametrical deflection for a spherical object having a diameter of 1.58 inches.
The term xe2x80x9cfluid,xe2x80x9d as used herein, includes gases, pastes, liquids, gels, or any combination thereof.
As used herein, the term xe2x80x9cfillersxe2x80x9d includes any compound or composition that can be used to vary the density and other properties of the subject golf ball core.
The term xe2x80x9cabout,xe2x80x9d as used herein, should be understood to refer to both numbers in a range of numbers.